At the least, once a year.
This can vary between people with certain partners and such. You should test before symptoms appear because usually, once symptoms appear, it is too late to be cured or treated.
Every six months can be frequented and sometimes preferred but is not required. Once a year is the least a person could do to test for STD's.
Hope this helps!
Non-infectious or non-communicable diseases are not able to be spread from one person to another.
